Voice over Internet Protocol (VOIP) is a technology that allows persons to send and receive voice, fax and data information over a combination of a phone network and a digital communications network. In traditional circuit switched networks such as a phone network, when a communication is established, a channel is dedicated end-to-end for the duration of the communication. Any unused bandwidth within the channel is unusable until the call is terminated. Research has shown that approximately sixty percent of a speech-based call is silence, thus a large portion of the bandwidth of a phone network is wasted. This is directly contrary to packet networks, wherein many types of communications share the bandwidth of the packet network. The capacity of the packet network is filled much more effectively in packet switched networks. Voice activity detection (VAD) technologies used in preparing voice signals for transporting across a packet network eliminate the silent space of a VOIP call in order to save more bandwidth, and speech compression technologies reduce the amount of data that must be transmitted when voice activity is present. By merging voice with the Internet or with an Intranet within an enterprise, the long distance telephone network and associated toll charges may be bypassed all together.
In a VOIP environment voice signals are processed for transport over a packet network. The VOIP environment includes a pair of gateways, one at each end of the packet network. The gateways perform the compression and packetizing necessary to accomplish VOIP. The voice signal is received by a first gateway, where the voice signal is then compressed and packetized. The packets are sent out on the packet network. The packets are received by the second gateway from the packet network. The second gateway converts the packets back into a voice signal.
The protocols that define a data network were originally designed for non-real time traffic. In traditional digital packet networks, when a router or switch becomes overloaded with packets, the router or switch may drop packets in order to relieve the congestion. The end protocols have methods built into them to account for the dropped packets by routers and switches within the network such that data integrity is maintained, such as by requesting retransmission.
A VOIP call can be considered a logical entity having 1 to n call legs. A call leg is a portion of a VOIP call. A call leg is made up of protocol messages. An endpoint is either the starting point of a call or the terminating point of a call. An endpoint can be either on net (inside the customers network) or off net (outside the customers network.)